Recovery of titanium metal values

ABSTRACT

Titanium metal values may be recovered from titanium and iron bearing sources such as an ilmenite ore by subjecting the source to an oxidation treatment and a reductive roast after having crushed the source to a desired particle size. The reduced source is then leached by treatment with a halogen-containing compound to form soluble titanium halides and iron halides. Thereafter the soluble titanium halide is precipitated as titanium dioxide by treatment with an iron oxide such as ferric oxide and recovered. The amount of titanium dioxide which is recovered is determined by the amount of reductant utilized in the reductive roast.

BACKGROUND OF THE INVENTION

Titanium in metallic form or as a compound is an important element inthe chemical series. For example, titanium dioxide is utilized in paintpigments, in white rubbers and plastics, floor coverings, glassware andceramics, painting inks, as an opacifying agent in papers, etc. Theother titanium compounds are used in electronics, as fire retardants,waterproofing agents, etc. The metal may be used as such or in alloyform as structural material in aircraft, in jet engines, marineequipment, textile machinery, surgical instruments, orthopedicappliances, sporting equipment, food handling equipment, etc. Heretoforein recovering the titanium from titanium bearing sources such asilmenite, rutile, etc., the titanium has been subjected to separationsteps which involve the formation of titanium as a compound in a valencestate of +4, such compounds usually involving titanium oxide. However,when attempting to separate titanium dioxide from impurities which arealso contained in the ore such as iron, the hydrolysis of the titaniumdioxide at elevated temperatures usually results in also obtainingrelatively large amounts of iron along with the titanium.

Heretofore in the prior art various methods have been utilized torecover titanium values from titanium bearing sources. For example, inU.S. Pat. No. 3,235,596 an unroasted ilmenite ore is leached withhydrogen chloride at an elevated temperature. Following this, dissolvediron is reduced with iron or other reductants to precipitate ferrouschloride by saturating the liquor with hydrogen chloride gas. Thehydrogen chloride is then extracted from the liquor by a vacuumdistillation and the titanium is recovered by conventional means.Likewise, U.S. Pat. No. 3,825,419 reduces an ilmenite ore to produceferrous oxides. The reduced ore is then leached for about 4 hours undera moderate pressure thereby dissolving the iron in the acid along withabout 15% of the titanium. The iron is recovered as impure ferric oxideby spray roasting the solution while the insoluble leach product whichis primarily titanium dioxide but which contains all of the silicapresent in the original ore is recovered. U.S. Pat. No. 3,859,077 alsodiscloses a process for recovering titanium in which a titaniumtetrahalide is mixed with iron oxide in slag or a titaniferous ore at anextremely high temperature of about 1000° C. to produce volatileimpurity chlorides and titanium dioxide. A similar patent, U.S. Pat. No.3,929,962, also reduces a titanium bearing ore at a high temperature toproduce titanium sesquioxide which is in a form whereby it is easier totreat for a titanium-iron separation. Another prior art reference, U.S.Pat. No. 3,903,239 teaches a method for recovering titanium in whichunroasted ilmenite is leached over a period of days at room temperatureto recover about 80% of the titanium. Sulfur dioxide is added during theleach process to cause a precipitation of the ferrous chloride afterwhich titanium dioxide is recovered by diluting and heating thesolution. U.S. Pat. No. 3,076,692 also discusses the problem ofminimizing the loss of titanium when leaching to produce titanium in a+4 valence state. The process described in this reference attempts toovercome the loss problem by utilizing a relatively short leach time,i.e., 10-20 minutes, or by adding phosphorous compounds.

In contradistinction to the prior art methods hereinbefore set forth forrecovering titanium metal values from a titanium bearing source, it hasnow been found possible to effect a titanium value recovery from asource such as ilmenite in such a manner so that the loss of titanium isminimal in nature.

This invention relates to a process for obtaining titanium values from asource which contains iron and titanium. More specifically, theinvention is concerned with a process whereby the loss of titaniumduring the various steps of the process is minimized, thereby assuring amore complete recovery of the desired product. By utilizing the processof the present invention, it is possible to allow virtually completedissolution of ilmenite ores in hydrochloric acid, the dissolved metalhalides being stable at relatively high temperatures for a longer periodof time than was heretofore possible. For example, by utilizing theoperating parameters of the leach solution it is possible, if sodesired, to effect the leach at a relatively high temperature, that is,about 100° C. for a period of time which may range up to about 2 hoursin duration without the attendant loss of titanium.

However, by utilizing operating parameters of the type hereinafter setforth in greater detail, it is possible to effect the leach of thetreated ore in a relatively short period of time, that is, about 0.25hours to about 0.5 hours in duration. In addition, excessively highroasting temperatures as well as relatively long periods of roast areavoided along with the attendant use of normal roasting equipment.Another advantage which may be found by utilizing the process of thepresent invention is that it is not necessary to submit the ore to agrinding operation whereby the particle size of the ground ore isexcessively small in order to obtain a high recovery of titanium.

It is therefore an object of this invention to provide an improvedprocess for the obtention of desired titanium metal values.

A further object of this invention is to provide a hydrometallurgicalprocess for obtaining high yields of titanium metal values in aneconomical manner.

In one aspect an embodiment of this invention resides in a process forthe recovery of titanium metal values from a titanium and iron bearingsource which comprises the steps of crushing said source, subjectingsaid crushed source to an oxidation treatment with an oxidizing agent atan elevated temperature, subjecting said crushed source to a reductiveroast in the presence of a reductant at an elevated temperature,leaching the resultant reduced source with a leach solution comprising ahalogen-containing compound separating insoluble gangue from the solublemetal halides, precipitating titanium dioxide from the soluble metalhalides by treatment with iron oxides, and separating and recoveringsaid titanium dioxide, the improvement in said process which compriseseffecting said reductive roast in which said reductant is present in anamount of from about two to three times the amount which isstoichiometrically required to reduce the iron oxide present in saidsource to metallic iron.

A specific embodiment of this invention is found in a process for therecovery of titanium metal values from a titanium and iron bearingsource which comprises crushing said source, subjecting the crushedsource to a reductive roast in the presence of a reductant which ispresent in an amount of from about two to about three times the amountwhich is stoichiometrically required to reduce the iron oxide present insaid source to metallic iron at a temperature in the range of from about600° to about 900° C., leaching the resultant reduced source with aleach solution comprising hydrogen chloride, separating insoluble ganguefrom the soluble metal chlorides, precipitating titanium dioxide fromthe soluble metal chlorides by treatment with iron oxides and separatingand recovering said titanium dioxide.

Other objects and embodiments will be found in the following detaileddescription of the present invention.

As hereinbefore set forth the present invention is concerned with aprocess for improving the yields of titanium metal values from atitanium bearing source. In addition to improving the percentage oftitanium extracted in the leach step of the operation, it is alsopossible to effect the leaching of the ore to form titanium in a +3valence state such as titanium trichloride and iron in a +2 valencestate such as ferrous chloride in the solution without requiring theformation of titanium in a +3 state by roasting. The obtention of highextraction of titanium is effected by utilizing certain improvements inan overall process, the improvements being obvious in the discussion ofthe process in greater detail.

The overall process for the recovery of titanium metal values from atitanium bearing source such as an ilmenite ore or a beach sand whichcontains iron as well as other metal values such as vanadium, chromium,manganese, etc., comprising crushing said source to a particle size inthe range of from about 35 mesh to about 100 mesh (Tyler). The crushingof the titanium bearing source may be effected in any suitable apparatussuch as a ball mill, etc. Following the crushing or grinding of the oreto the desired size, the ore is then oxidized by treatment with anoxidizing agent such as an oxygen-containing gas such as air, oxygen,etc., at an elevated temperature less than that which is required toform pseudobrookite. Generally speaking, the temperature at which thesource is subjected to the oxidation treatment will be in a range offrom about 700° to about 900° C. for a period of time which may rangefrom about 0.5 up to about 2 hours.

Following this the crushed metal bearing source in which the iron whichis present has been oxidized to ferric oxide is then subjected to areductive roast at an elevated temperature whih may range from about600° up to about 900° C. or more in the presence of a reductant. Thereductant or reducing agent is gaseous in form and will comprisehydrogen, carbon monoxide, combinations of carbon monoxide and hydrogen,etc., said reducing treatment being effected for a period of time whichmay range from about 0.5 up to about 2 hours or more in duration. It hasnow been discovered that the amount of reductant which is employed inthe reducing step of the operation is critical and therefore the amountto be used is based on the stoichiometric amount which is required toreduce the iron to a metallic state. In the preferred embodiment of theinvention the amount of reductant employed is in a range of from abouttwo to about three times the amount of reductant which isstoichiometrically required. By utilizing this amount of reductant, itis possible to minimize the resultant loss of titanium as insolubleproducts in the subsequent leach step of the operation with a concurrentoptimum dissolution of the titanium content of the ore as titaniumhalide in said leach step. In the preferred embodiment of the inventionthe reducing atmosphere which is used to accomplish the purpose of theroast usually comprises a mixture of about 50% carbon monoxide and 50%hydrogen.

After reductively roasting the metal bearing source the reduced sourceis then subjected to an aqueous leach which, in the preferred embodimentof the invention comprises an aqueous hydrogen halide solution. Thepreferred hydrogen halide which is employed in the reaction compriseshydrogen chloride, although other hydrogen halides such as hydrogenbromide and hydrogen iodide may also be utilized, although notnecessarily with equivalent results. The aforesaid leach of the metalbearing source is usually effected at a temperature which may range fromabout ambient to about 110° C., the preferred range being from about 80°to about 100° C., for a period of time ranging from about 0.25 hours upto about 1 hour or more in duration.

Following the leach of the metal bearing source which will form solubleiron halides and titanium halides such as ferrous chloride, titaniumtrichloride, etc., the mixture is subjected to a separation step inwhich the solid gangue is separated from the soluble metal chlorides anddiscarded. The separation of the solid gangue from the soluble metalchlorides may be effected in any suitable manner by means well known inthe art, said means including decantation, filtration, etc. The solublemetal halides are then subjected to a precipitation step in aprecipitation zone wherein the aqueous metal halides such as titaniumtrichloride and ferrous chloride are subjected to reaction with an ironoxide, preferably one in which the iron is present in its highestvalence state such as ferric oxide. In this precipitation zone where thetreatment is effected at temperatures ranging from about 80° to 110° C.,the iron oxide such as ferric oxide will react with titanium trichlorideto form solid titanium dioxide. This compound, after separation from thesoluble iron halides in a solid/liquid separation zone, will berecovered as such and may thereafter be treated to recovery as titaniummetal, if so desired. Following separation of the solid titanium dioxidefrom the soluble ferrous chloride, the latter is passed to acrystallization zone wherein the temperature is reduced to affordcrystallization of the ferrous chloride. For example, the temperature atwhich the crystallization or precipitation of the ferrous chloride iseffected may range from about 0° to slightly in excess of ambient or, inextreme cases, up to about 90° C. When utilizing subambient temperaturesthe cooled solution is maintained in the desired subambient by externalmeans such as an ice bath, cooling coils, etc. After crystallization ofthe ferrous chloride is completed, the solids are separated from theleach liquor which may be recycled back to the leach zone. The solidferrous chloride is recovered and a major portion of the product issubjected to a direct reduction step which is effected at an elevatedtemperature in the range of from about 600° to about 900° C. in contactwith an excess of hydrogen. In this direct reduction step, the metalliciron which is produced will be in the form of powder or crystals and maybe recovered as such. In addition, the hydrogen chloride which is formedduring the direct reduction of the ferric chloride to metallic iron iswithdrawn and recycled to the leach step of the process to make up aportion of the leach solution. While a major portion of the ferrouschloride in an amount ranging from 50% to 90% is subjected to thisdirect reduction, the remaining portion in an amount ranging from about10% to about 50% is subjected to an oxidation step. In the oxidationstep the ferrous chloride is treated at an elevated temperature rangingfrom about 300° to about 800° C. by contact with an oxygen-containinggas such as air or oxygen, the preferred oxidizing agent comprising airdue to its greater availability and negligible cost. Any hydrogenchloride which may be formed during the oxidation step is recycled tothe ferrous chloride crystallization zone to saturate said zone in orderto insure a complete precipitation of the ferrous chloride by reducingthe solubility of said compound. In the oxidation zone the reaction ofthe ferrous chloride with an oxidizing agent results in the formation ofiron oxides such as ferrous oxide, ferric oxide, these compounds beingcharged to the zone containing the titanium trichloride where saidtitanium trichloride is contacted with the iron oxides to form titaniumdioxide.

The process of the present invention may be effected in any suitablemanner and may comprise either a batch or continuous type operation. Forexample, when a batch type operation is used a titanium bearing sourcesuch as ilmenite ore which has been crushed or ground to the desiredparticle size is subjected to an oxidation treatment. In the oxidationtreatment the ore is contacted with an oxygen-containing gas such as airat an elevated temperature within the range hereinbefore set forth for apredetermined period of time. Following the oxidation treatment the oreis then subjected to a reductive roast. In the reductive roast the oreis contacted with a reducing agent such as a mixture of carbon monoxideand hydrogen also at a temperature within the range hereinbefore setforth and for a predetermined period of time. The amount of reducingagent which is utilized as the reductant will be determined within adesired range and generally will be present in the reduction zone in anamount in the range of from about two to three times the amount ofreducing agent which is stoichiometrically required to reduce the ironoxides present in the ore to metallic iron. Thereafter the reduced oreis then placed in an appropriate apparatus where it is contacted with aleach solution which, in the preferred embodiment of the invention,comprises an aqueous hydrogen chloride solution. After completing theleach which may be effected at temperatures ranging from ambient up toabout 110° C., the solid material comprising gangue and/or otherinsoluble metal compounds is separated from the leach liquor, the latterthen being placed in an apparatus wherein it is contacted with ironoxides, and preferably ferric oxide, at an elevated temperature rangingfrom about 80° to about 110° C. After formation and precipitation oftitanium dioxide by treatment with the ferric oxide, the solid titaniumdioxide is separated from the leach liquor and recovered. The leachliquor is treated to precipitate ferrous chloride which may then betreated by a direct reductive step to recover metallic iron and hydrogenchloride or, in the alternative, it may be subjected to an oxidationstep to produce ferric oxide which can be reused in the treatment of thesoluble titanium chloride to form the desired titanium dioxide.

As an alternative method of recovering the desired product, the leachliquor which contains the soluble ferrous chloride and titanium chlorideafter separation from the solid gangue material may be placed in anapparatus which is maintained at a temperature lower than that at whichthe leach is effected. The result of this lowering of the temperaturewill be the formation of crystalline ferrous chloride. Aftercrystallization of the ferrous chloride is complete, the solubletitanium chloride may be separated from the crystals by conventionalmeans such as filtration, decantation, etc., and the solution thentreated with ferric oxide in a manner similar to that hereinbefore setforth to form titanium dioxide which is then separated and recovered.The solid ferrous chloride obtained in the previous precipitation stepmay then be subjected to a direct reduction by treatment with hydrogenat an elevated temperature to again form metallic iron and hydrogenchloride or to an oxidation process by treatment with anoxygen-containing gas at an elevated temperature to form ferric oxide.

It is also contemplated within the scope of this invention that theprocess may be effected by utilizing a continuous method of operation.When utilizing the continuous method of operation the ore, which hasbeen crushed or ground in a crushing zone to the desired particle size,is continuously fed to an oxidation zone wherein the ore is contactedwith the oxygen-containing gas at an elevated temperature. After passagethrough the oxidation zone the ore is continuously fed to a reducingzone wherein the ore is subjected to a reductive roast utilizing areductant usually comprising either hydrogen, carbon monoxide, or acombination thereof. The reductant is also continuously charged to thiszone at a rate which is sufficient to maintain the amount of reductantpresent in the zone in a range of from about two to about three timesthe amount which is stoichiometrically required to reduce the ironoxides to metallic iron. After passage through the zone for apredetermined period of time the reduced ore is continuously withdrawnand passed to a leaching zone wherein it is subjected to a leachtreatment with a hydrogen halide such as an aqueous hydrogens chloridesolution. After passage through the leaching zone the pregnant leachliquor containing dissolved metal chlorides along with undissolvedsolids such as gangue or insoluble metal compounds is continuouslywithdrawn and passed to a filtration zone or separation zone wherein thesoluble metal halides are separated from the solids. After passagethrough the filtration zone the pregnant leach liquor is continuouslypassed to a precipitation zone wherein the leach liquor is contactedwith ferric oxide to effect a precipitation of titanium dioxide. Themixture of solid titanium dioxide and leach liquor containing solubleferrous chloride is continuously withdrawn after passage through thezone to a solid/liquid separation zone wherein the solid titaniumdioxide is separated and continuously withdrawn from the leach liquorand passed to storage.

The leach liquor is also continuously withdrawn from the separation zoneand passed to a crystallization zone which is maintained at a lowertemperature than that of the previous zones. In the crystallization zonethe ferrous chloride crystallizes out of the leach liquor which iscontinuously withdrawn and recycled to the leach zone. The solid ferrouschloride in crystalline form is continuously withdrawn from this zoneand may, if so desired, be passed to a reduction zone wherein itundergoes the direct reduction in the presence of hydrogen to formmetallic iron. Metallic iron which is formed in the reduction zone iscontinuously withdrawn and passed to storage while the hydrogen chloridewhich is formed during the reduction is also continuously withdrawn andrecycled to the leaching zone to form a portion of the leach solution.In the alternative, if so desired, the ferrous chloride which has beenwithdrawn from the crystallization zone may be passed to an oxidationzone wherein it is contacted with an oxygen-containing gas at anelevated temperature to form a mixture of iron oxides, namely, ferricoxide. These compounds are continuously withdrawn from the oxidationzone and passed to the precipitation zone hereinbefore set forth forcontact with the pregnant leach liquor to effect the formation of solidtitanium dioxide. Any hydrogen chloride which is formed during thereaction in the oxidation zone is also continuously withdrawn and passedto the crystallization zone wherein it is used to saturate the zone toreduce the solubility of the ferrous chloride contained therein.

In the event that an alternative method of effecting the entire processof this invention is desired, the leach liquor which contains dissolvedmetal chlorides, after separation from undissolved solids such asgangue, etc., is continuously withdrawn from the separation zone andpassed to a crystallization zone which is maintained at a temperaturelower than that of the leach zone. In the crystallization zone theferrous chloride crystallizes out of the leach liquor, the latter thenbeing continuously withdrawn while the solid ferrous chloride is treatedin a manner similar to that hereinbefore set forth, that is, either bydirect reduction to metallic iron or an oxidation to ferric oxide. Theleach liquor which is continuously withdrawn from the crystallizationzone is then passed to a precipitation zone wherein it is contacted withferric oxide which is also continuously charged to the precipitationzone. After formation of solid titanium dioxide in this precipitationzone, the desired product is separated from the liquor and passed tostorage.

The following examples are given for purposes of illustrating theprocess of this invention. However, it is to be understood that theexamples are given merely for purposes of illustration and that thepresent process is not necessarily limited thereto.

EXAMPLE I

To illustrate the requirement that the amount of reductant which is usedin the reductive roast step of the process be within a range of the typehereinbefore set forth, an ilmenite ore from Telemark, Norway wascrushed to about -35 mesh. Samples of the crushed ore were placed in aquartz furnace tube and subjected to an oxidation treatment by passing astream of moist air over the ore for periods of 30 to 60 minutes whilemaintaining temperatures of from 650° C. to 900° C. At the end of thistime period the furnace tube was purged with nitrogen to flush out themoist air and thereafter the ore was subjected to a reductive roast bypassing various amounts of carbon monoxide and hydrogen over the ore attemperatures of 650° to 900° C. The reductive roast was effected duringperiods of 0.5 to 2 hours at the end of which time the ore was allowedto cool to room temperature under a nitrogen flow.

The reduced ore was then leached by mixing 50 grams of the ore with 300ml of hydrochloric acid in a flask and heating the mixture to 100° C. Atthe end of the 15 minute period the leach liquor was separated from thesolids by filtration and allowed to cool to room temperature. The leachliquor was analyzed to determine the amount of titanium which had beenextracted from the ilmenite ore. Analysis disclosed that in a series ofruns in which 1.5 times the amount of reductant which wasstoichiometrically required to reduce the iron oxides present in the oreto metallic iron resulted in an average of 58% of the titanium presentbeing extracted in the leach liquor. A second series of experiments inwhich the amount is carbon monoxide and hydrogen which was passed overthe ore amounted to 4.5 times the amount stoichiometrically required toreduce the iron resulted in a 47% extraction of the titanium. Incontradistinction to this, when the amount of carbon monoxide andhydrogen which was passed over the ore during the reductive roastamounted to three times the amount stoichiometrically required to reducethe iron oxides to metallic iron a 75% extraction of the titanium wasobtained.

EXAMPLE II

In this example 70 grams of an ilmenite ore which was ground to -65 meshwas subjected to an oxidation treatment by passage of air over the oreat a temperature of 900° C. Following the oxidation treatment the quartztube in which the ore was positioned was purged with nitrogen andreduced by passage of hydrogen over the ore at a temperature of 700° C.Both the oxidation and reduction steps were performed during a period of60 minutes. At the end of the 60 minute period the ore was allowed tocool to room temperature while maintaining a flow of nitrogen over saidore. The ore was recovered and 50 grams leached by treatment with 300 mlof hydrogen chloride for a period of 15 minutes while maintaining thetemperature of the leach solution at 100° C. The solids were thenseparated from the pregnant leach liquor by filtration. When the amountof hydrogen which was passed over the ore amounted to twice the amountnecessary to stoichiometrically reduce the iron oxides to metallic ironthere was obtained a 44% extraction of the titanium. Incontradistinction to this when five times the amount of hydrogenstoichiometrically required to reduce the iron oxides to iron was passedover the ore only 24% of the titanium was extracted.

It is therefore readily apparent from the above examples that when theamount of reducing agent or reductant which is passed over the oreduring the reductive roast is in a range of from about two to aboutthree times the amount stoichiometrically required to reduce the ironoxides to metallic iron it is possible to obtain a greater extraction ofthe titanium which is present in the pregnant leach liquor as titaniumtrichloride with a concommitant minimal loss of titanium which remainsin the solid portion of the leach mixture as titanium dioxide.

I claim as my invention:
 1. In a process for the recovery of titanium metal values from a titanium and iron bearing source which comprises the steps of:(a) crushing said source; (b) subjecting said crushed source to an oxidation treatment with an oxidizing agent at an elevated temperature; (c) subjecting said crushed source to a reductive roast in the presence of a reductant at an elevated temperature; (d) leaching the resultant reduced source with a leach solution comprising hydrogen chloride; (e) separating insoluble gangue from the soluble metal chlorides; (f) precipitating titanium dioxide from the soluble metal chlorides by treatment with iron oxides; and (g) separating and recovering said titanium dioxide, the improvement which comprises using as said reductant in said reductive roast step (c) a mixture of about 50% carbon monoxide and 50% hydrogen in an amount of from about two to three times the amount which is stoichiometrically required to reduce the iron oxide present in said source to metallic iron and the following recovery of titanium dioxide in step (g) reducing the temperature of the solution remaining to crystallize ferrous chloride, recovering the solid ferrous chloride, reducing a major portion of said ferrous chloride to form metallic iron and hydrogen chloride, recovering the iron and recycling the hydrogen chloride to leach step (d) as a portion of the leach solution, oxidizing the other portion of said ferrous chloride to form iron oxides and recycling said oxides to step (f).
 2. The process as set forth in claim 1 in which the oxidation treatment is effected at a temperature in the range of from about 700° to about 900° C.
 3. The process as set forth in claim 1 in which the reductive roast is effected at a temperature in the range of from about 600° to about 900° C.
 4. The process as set forth in claim 1 in which said oxidizing agent is air.
 5. The process as set forth in claim 1 in which said oxidizing agent is oxygen. 